Clarity on Antarctic sea ice.

I’ve always been a skeptic when it comes to Antarctic sea ice. I’m not referring here to the tiresome (and incorrect) claim that the expansion of sea ice around Antarctica somehow cancels out the dramatic losses of sea ice in the Arctic (NB: polar bears don’t really care if there is sea ice in Antarctica or not). Rather, I’m referring to the idea that the observation of Antarctic sea ice expansion represents a major conundrum in our understanding of the climate system, something one hears even from knowledgeable commentators. In this post, I’ll try to provide some clarity on this subject, with some basic background and discussion of a couple of important recent papers.

In general, Antarctic sea ice forms near the coastline, where upwelling waters cool to the atmosphere. It melts when the winds and currents push it into areas of warmer water to the north. In the summer, it melts pretty much all the way back to the coast. An efficient way to form lots of Antarctic sea ice during the autumn growth season is to have strong winds that push the ice away from the coastline. Pushing sea ice away leaves open water that can lose heat to the atmosphere, creating more sea ice. The persistent circumpolar westerlies are critical in pushing ice toward the north, into warmer waters. (Owing to the Coriolis effect, westerly winds cause northward-flowing surface ocean currents in the Southern Hemisphere).

The importance of the winds in controlling Antarctic sea ice leads to the obvious idea that changing winds can explain the increase that has been observed over the last several decades. There has indeed been a substantial increase in the circumpolar westerlies; this is very well established from observations and is associated with the oft-discussed increase in the “Southern Annular Mode” (SAM) index2. Averaged over the year, the SAM index has increased nearly monotonically since the 1970s (e.g., Marshall et al., 2003). This has led to a fairly simple logic in explaining the recent sea ice increase: the westerly winds have increased, so sea ice has increased too. Furthermore, there is good evidence that the increasing westerlies are a response to anthropogenic climate forcing from CO2 and other greenhouse gas increases in the troposphere, along with ozone declines in the stratosphere (Thompson and Solomon, 2002; Thompson et al., 2011). This would suggest that the observed increase in Antarctic sea ice extent is anthropogenic in origin, just like the Arctic sea ice decline, but for very different reasons. In short, reduced ozone in the stratosphere, and increased CO2 in the troposphere — both climate forcings that are unequivocally anthropogenic — cause increased westerly winds, which cause Antarctic sea ice to expand.

Of course, it’s not that simple. For one thing, the average increase of Antarctic sea ice is actually a small number that is the difference of two big numbers — modest increases over a large area, mostly in the Eastern Hemisphere, and very large decreases over a smaller area in the Western Hemisphere. The map below, showing change in the length of the sea ice season over the last 30 years, illustrates this point well. In spite of the average increase, there are very rapid declines in the Bellingshausen and Amundsen Seas, comparable to sea ice declines in the Arctic. Furthermore, the only season is which there is a significant trend in the westerlies is austral summer. There is a weak positive trend in fall, but both spring and winter show no trend; the SAM trends in these seasons may even be slightly negative, depending on which data are used (Ding et al., 2012). Yet the pattern of sea ice change is quite similar in all seasons: decreasing along the Pacific coast of West Antarctica, and increasing around most of East Antarctica, and in the Ross and Weddell Seas.

Trend in the length of the sea ice season, 1979-2010. Blue and purple areas show areas where sea ice is declining, orange and red where it is increasing. Source: Maksym et al., 2012

On top of these subtleties, confusion about the role of the winds has arisen because some of the prominent modeling studies that have examined the relationship between the westerly winds and Antarctic sea ice have come up with results that appear to be in direct opposition to the observations. When fully coupled climate models are run with increased CO2 and decreased stratospheric ozone, the westerly winds increase as has been observed, but sea ice decreases around most of Antarctica. For example, Bitz and Polvani, 2012 found that the pattern of trends is the mirror image of the observations, with increases, rather than decreases in the Amundsen and Bellingshausen Seas.

So what’s really going on? One idea is that changes in ocean stratification might be important. There has been a huge increase in the amount of fresh water getting into the Southern Ocean from melting glaciers, especially in the Amundsen Sea (see, e.g., the latest data from Sutterly et al., 2014). Fresh water forms a sort of buoyant lid on the ocean, limiting the ability of heat from the warmer water below to get to the sea ice and melt it. A study by Bintanja et al. (2013) showed that it was a least plausible that this explains the Antarctic sea ice change. A basic problem, though, is that the greatest discharge of meltwater is occurring in the Amundsen Sea, exactly where sea ice is declining, so while this probably is part of the story, I doubt it’s very dominant.

As it turns out, comparing observations with the results of model experiments like those of Bitz and Polvani (2012) is misleading. Most such experiments are equilibrium experiments: What’s done is to run a model under “preindustrial” conditions, and then to run it again with reduced ozone and increased CO2, and to look at the difference. This provide a measure of what will eventually happen (at least in the model) after many decades or centuries. But when you look at the transient response to changes in the circumpolar winds, as Marshall et al (2014) have done, it turns out that two important things happen. The winds tend to push the sea ice boundary northward, as we would have expected. But the winds push the surface ocean northward too, and cause a slow rise in the isopycnal surfaces (surfaces of constant density). This brings relatively warm deep water closer to the surface, eventually melting sea ice after a period of a few decades, countering the initial increase in sea ice. These results explain why equilibrium model calculations find sea ice decreasing in response to ozone forced changes in the circumpolar winds, and also why observations show the opposite. Not enough time has passed for the equilibrium response to be manifested. These results suggest that some time in the next few decades, there will reverse, and average sea ice will begin to decline.

Furthermore, there’s a whole lot more going on with the winds than just “increased westerlies”. In the areas where the big sea ice losses have occurred, the concept of “circumpolar westerlies” isn’t very relevant. A far more important measure of wind variability in the Amundsen and Bellingshausen Seas is the Amundsen Sea Low (ASL).5 The ASL describes the average location of storms systems the bring heat and moisture into West Antarctica. Changes in the ASL may occur for myriad reasons, but one big hammer that can make it ring is the propagation of atmospheric planetary wave arising out of the tropics, more-or-or less associated with ENSO (El Niño-Southern Oscillation) variability. It’s been clear for many years that ENSO variability play a significant role in sea ice variability in those regions, and recent work shows that this can explain the trends pretty well too (e.g. Yuan and Li, 2008; Stammerjohn et al., 2008). Not incidentally, the adjacent land areas of the Antarctic Peninsula and the West Antarctic Ice Sheet have warmed significantly over the last few decades (Steig et al, 2009;Orsi et al., 2013; Bromwich et al, 2013), and those changes can also be attributed largely to tropical climate variability (Schneider and Steig, 2008; Ding et al., 2011; Schneider et al., 2012; Steig et al., 2013). The cause of temperature and sea ice change is the same: more warm air is being steered into West Antarctica, and the atmospheric flow tends to push sea ice against the continent, keeping it from expanding.

So, do we get the right answer if we take into account all of the wind changes that have occurred over the last few decades? The answer is yes. This is nicely illustrated in a study by Holland and Kwok (2012), who showed that wind, ice motion, and ice concentration changes match each other remarkably well. Where the wind has been increasingly northward, concentrations are increasing; where wind and ice motion changes are toward the continent, ice concentrations are decreasing. And this year, Holland et al. (2014), showed that when they drive an ocean and sea ice model with observed winds — not just increased westerlies, but the full range of wind changes, as calculated by the ECMWF (European Center for Medium Range Weather Forecasting) –- they correctly simulate the overall expansion of sea ice, and they also get the pattern of changes pretty much spot-on. To be sure, the authors note that not all the details are explained, and they highlight the possibly greater importance of thermodynamic consideration (i.e. ocean temperature/stratification) in some areas than in others. Also, the period they study (1992-2010 only) is pretty short. The results are nevertheless pretty compelling. Just like the observations, the calculations show large decreases in the Amundsen and Bellinghausen seas, but increases nearly everywhere else.7

Taken as a whole, these results show that there is no significant contradiction between our understanding of Antarctic sea ice and the observation that it is, in average, expanding. We can explain sea ice trends in the Antarctic rather well if we take into account the full range of changes in winds that have occurred. The average expansion of Antarctic sea ice was not anticipated, but it hardly represents any sort of existential threat to our fundamental understanding of the climate system as a whole. It’s merely an interesting scientific challenge.

Not incidentally, changing winds also have a lot to do with what’s been happening to the Antarctic ice sheet (meaning the land-based glaciers, distinct from the sea ice). I’ll have another post on that later this month, or in the New Year.

@50 “In today’s financial world, experts would be laughing off folks that still maintain that their model and its prediction are still sound, despite being wrong so soon after initialization (conceptually what should be its most accurate time-frame).”

Yet in today’s financial world, experts are routinely egregiously wrong, and still taken seriously. You mention Paul Krguman, so surely you know how he mocks those who predicted hyper inflation, which never happened. Yet these same charlatans continue to be taken seriously, and some are even professors. You compare climate scientists to finance to show just how out of touch the climate scientists are to those always-right, factual finance gurus, who could even predict our last recession.

If you want to criticize the accuracy of models on antarctic ice loss, I think it would be better to not use bogus comparisons, or to just skip the rhetoric all together.

#50–No, in the post it is not “model trends” which are reversed; it is:

…the pattern of trends… with increases, rather than decreases in the Amundsen and Bellingshausen Seas.

I don’t think there is any ‘concession’ involved in saying that the models don’t accurately produce observed ice trends. That was the topic of this whole post, after all.

As to your ‘real question,’ you ask three questions. Which one is ‘real?’ If it’s one of the two that boil down to ‘When will climate models accurately characterize current observations?’ how on Earth is Dr. Steig, or anyone, for that matter, supposed to know the answer?

As the post shows, it’s a knotty problem, with multiple teams tackling it. Someone could crack it next Tuesday, or it may take another ten years.

Yes, models have problems. And the mismatch with Antarctic sea ice observations might indeed point to potential improvements.

There are different kinds of models (heuristic, curve-fitting, physics-based and so forth) with different purposes. It’s important to understand the differences and it’s not clear what you’re talking about, especially when you refer to macroeconomic or financial models.
You shouldn’t simply assume about a model that “soon after initialization” is “conceptually what should be its most accurate time-frame”. Or that certain GCMs “are tasked with predicting Antarctic Sea Ice trends”.
Since you mentionned “the larger overall picture of anthroprogenic global warming”, you may be talking about the type of GCM typically discussed here or in the IPCC report. These are not made for weather forecasts and the “most accurate time-frame” isn’t supposed to be “soon after initialization”. These models are relying for their skillfullness on large-scale energy flows which have imbalances all the time but must balance in the long run. They are don’t need to be able to predict transcient features of the system.
If you are for some reason concerned about projections involving Antarctic sea ice declines in 2100, you ought to look at what causes these modelled decreases and in particular whether any modelled changes in Antarctic sea ice are themselves a major driver. Because if the major drivers by 2100 aren’t local, a model might well be very wrong about local variations shortly after initialization before getting it basically right once a global effect overwhelms local variations.

“Polar bears don’t really care if there is sea ice in Antarctica or not” Ok but where is the evidence they care about Arctic sea ice? We have done more for Polar bears by restricting hunting than any threat from lower sea ice in the summer. The proposition that the lower sea ice we have seen over the last decades is something polar bears have never seen over the 1000s of years they have lived in the arctic does not pass common sense tests. Geologic records show trees on the arctic coasts in past warm periods. Polar Bears made it through those periods.

Tasty bait. Google this:
“key climatic events have played a significant formative role in bear effective population size.”

The polar bear studies have been under attack by the Arctic Sea oil interests for a few years now.. The top hit quoting that bit from recent academic work is the ‘advocacy science’ blog ‘World Climate Report’ for one example.

“Rates of reproduction and survival are dependent upon adequate body size and condition of individuals. Declines in size and condition have provided early indicators of population decline in polar bears (Ursus maritimus) near the southern extreme of their range. We tested whether patterns in body size, condition, and cub recruitment of polar bears in the southern Beaufort Sea of Alaska were related to the availability of preferred sea ice habitats and whether these measures and habitat availability exhibited trends over time, between 1982 and 2006. The mean skull size and body length of all polar bears over three years of age declined over time, corresponding with long-term declines in the spatial and temporal availability of sea ice habitat. Body size of young, growing bears declined over time and was smaller after years when sea ice availability was reduced. Reduced litter mass and numbers of yearlings per female following years with lower availability of optimal sea ice habitat, suggest reduced reproductive output and juvenile survival. These results, based on analysis of a long-term data set, suggest that declining sea ice is associated with nutritional limitations that reduced body size and reproduction in this population.”

Oh, it’s science, must be wrong …

Where is your evidence that the population ecologists who study polar bears are wrong?

Oh, unrestricted hunting was banned, right. The people studying polar bears know that, indeed they (or their professional forebearers) also did the studies showing that unrestricted hunting was driving polar bears to the edge.

#56
Must we play this game over and over and over? Previous changes occurred over many hundreds of years, giving the bears time to slowly adapt. Present changes are on a timescale of decades, giving little or no time to adapt. Hypothetical question: if your income were reduced to zero slowly over the next 10 years, would you be able to adapt better than if it were reduced to zero next week?

Under Occman’s razor one should look for the simplest explanation and, here, look for a direct link between North and South ice. An obvious possibility is the thermohaline circulation, which includes a direct pipeline down the Atlantic between the Arctic and Antarctic. Its cold, salty water runs South to Antarctica, then veers East, part going around Antarctica and part going up the East coast of Africa, upwelling in these areas. There is a strong trend toward more sea ice where the THC touches Antarctica. Also surface temperatures are cooling in those areas (but not SE Africa).

There is a strong statistical link between monthly percent changes in Arctic ice and changes in Antarctic ice, controlling for seasons. When ice extent declines more than usual in the North, it increases more than usual some 4 to 12 months later in the South (and visa versa). There is no similar impact of Southern ice changes on Northern ice changes, so it is a one-way effect and not a seasonal coincidence. This timing is consistent with the largest estimates of the speed of the Atlantic THC.

Why would Arctic temperature increases cause the THC to pump more cold water (or colder water) to Antarctica? One possibility is that the surface temperature increase (and the resulting salinity decrease) has strengthened and lowered the (weak) thermocline, such that surface water mixes less with the water that goes into the THC, leaving the surface water warmer and the deep water colder than in the past. The THC exports “coldness.” This might account for the fact that Arctic temperatures have risen faster than expected.

However, I don’t know of any research concerning whether the THC is sending more cold water South.

#59
spilgard says:
“Must we play this game over and over and over?
It would appear so.Let me put it this way,if you were told your income would be reduced to zero slowly over the next 10 years and it did not reduce for 18 years,at what point would you stop “adapting” and start asking questions?

@62 You are upside down on your analogy. The relevant analogy, since you are so very fond of cherrypicking, is what if your income had a disastrous near-zero year then recovered somewhat but continued to decline regardless? When would you begin to ask questions?

Someone asked over at Tamino’s whether wind pushing sea ice away, opening up new surface to freeze, wouldn’t also push the sea ice out to water warm enough to melt it. Do we have info on sea surface temperatures around the edge of the sea ice? I’d assume wind would push cold water, as well as ice.

Also, some of the ice is pushed into places where the thermohaline circulation is upwelling so the ice is encountering cold bottom water — right?

Has anyone thought of distributing some Argo floats on the coastal sea ice? They’d give position information, at least, and presumably temperature, until the ice they were on eventually melted — and then they’d take up their normal course in sea water, giving the salinity from that point on.

Or of course simply doing what’s done in the Arctic every winter, putting stations on the ice that drift and report where they are and the conditions over time, and then eventually sink.

Great chart in the article you cite shows methodologies used and results (Degree expansion per decade) of the “more than 30 studies” which now put the rate of expansion in the range you quote. Chart displays data collated from Lucas et al. 2014. Article gives overview with comment on methodologies.

Lucas et al. 2014 “The expanding tropics: a critical assessment of the observational and modeling studies” puts smmary of studies by methodology into several tables:

#62:
This is getting way off of the topic of Antarctic ice, but try to stay focussed. Post #56 is flogging the weary “climate’s changed before” talking point. You’re jumping over to the shopworn “global warming stopped in [xxxx]”.
I doubt that we’re thinking of the same thing, but I’m inclined to agree that you need to start asking questions. One of Tamino’s posts will help to give you a few questions to pose to the sellers of the “warming stopped” silliness:http://tamino.wordpress.com/2014/01/30/global-temperature-the-post-1998-surprise/

CUFC commented on salinity concerns and that was studied by Ukrainian researchers finding the desalination of the surface layer has complex relationships that seem to be positive feedbacks during warming. First, consider that the winds are blowing snow onto the sea surface, that freshens it and it freezes faster than seawater so thickens to insulate the sea.

So, as the water freezes there is less brine being produced and less dense, saline current flow to the main source of deep Antarctic current, that’s a long-term concern; and, with a less saline surface layer that evaporates easier thus more snow and even some rain falls on the continent. That becomes more runoff in summer near shore which freshens the surface layer, and in winter there has been an increase in snowfall as stated a positive feedback.

My first source for the topic is “The Antarctic Challenge” a DVD anthology on ongoing research; Keryogin (sp?) at Vernadsky Station focused on the fresh water issue.

Does anyone here have an opinion on the work being cherry picked, produced and collated by Ben Davidson (not a scientist) et al over at http://www.suspicious0bservers.org/ (web) and https://www.youtube.com/user/Suspicious0bservers ? Increasing Antarctic sea ice and volcanism under the Thwaites glacier is often cited… The basic thrust is a that anthropogenic forcing of climate is negligible – if that and the IPCC keep getting it wrong and that the sun and galactic energy bursts are the sole drivers of climate. The evidence and discussion, to this novice, is often compelling and plausible. I have now bookmarked this site and would greatly appreciate some commentary here. Thanks in advance

Russell,
Not sure how Mencken’s law applies to politics of climate, as the politicians are applying every tool in their considerable obstacle of obfuscation to divert attention from the credible threats.

In any case, Mencken’s law is incomplete–politicians must direct peoples’ attention toward the threats to which they claim to have “the answer,” not those about which they are utterly clueless.

Paul Bandurski,
Do the math. Geothermal fluxes, including volcanism are laughably tiny compared to increased greenhouse warming. I would suggest paying attention to what the experts say, rather than a bunch of amateur morons.

Paul Bandurski @72.
You are pointing us at a website stacked with videos of indeterminate length and with messages saying God-knows what. I could nto be fussed to investigate as the one video you specifically point us at and which is thankfully short proves to have an exceedingly short message. It couldn’t be shorter. It says zip!!
If you wish comment on your “galactic” outbursts, I suggest you start by being a little more specific about what you want folk to comment on.
I would caution you that the IPCC presents evidence that is a little more well founded than the guff you can expect from an egotistical fool like Ben Davidson. And there is already on-line rebuttals of Davidson, one in a trio of videos (12 mins, 19 mins and 11 mins long) which at least have easier music than Davidson’s videos.

–when Dr. Steig had set it to 500hPa with the MSLP overlay and responded:

[ … It makes for a nice, informative visualization of what matters in Antarctica. In particular, note how the low-pressure centers (red), rather than the circumpolar westerlies, dominate the wind field near Antarctica. …]

MARodger @ 76 Yes I am suspicious of Ben Davidson and thank you for the rebuttal videos. What I am trying to get my head around and, please correct me if I am wrong, is why is it that climatologists don’t look beyond the troposphere and take into account the energy inputs from space weather as being a significant driver of climate change?
There is a neat little interactive page here for monitoring extra solar system gamma-ray bursts: http://grb.sonoma.edu/
The magnetosphere is shrinking and National Geographic reported back in 2004 that it had shrunk by 10% since record keeping began. I would think that consequently, with this trend of a fading magnetic field, the earth would be receiving more energy and that this would be an important driver of climate?
I am suspicious too of the IPCC and the way it is used to drive the political agenda to blame humans and therefore tax us for global warming, the very warming that the IPCC has failed to predict for the last 15 years. Yes this is a mere nanosecond in the scheme of things, however, the point is that a warming trend is not yet clear. I don’t dismiss the anthropogenic quotient, however, I am trying to ascertain how significant it is in overall scheme of things. Yes I am a novice and do appreciate direction from knowledgeable folk here.

t. marvell @79.
I would beg to differ. Your post @61 makes claims of an arithmetic nature but doesn’t even explain what you are about, at least not with enough clarity for us here to understand your method. I did waste 10 minutes trying to find your “strong statistical link between monthly percent changes in Arctic ice and changes in Antarctic ice” and I even took the trouble to remove any seasonal signals (what I assume you call “controlling for seasons”) but that is when all statistical significance entirely dissappered.
So you have yet to reach first base in this matter. Do you then really believe you are in a position to demand folk explain themselves?

Paul Bandurski @78.
It is good to get to the bottom of what it is that concerns you. You appreciate that none of this has anything to do with the Antarctic which is the subject of this post.
I will reply briefly here, but this is ‘off-topic’ and further comment should really be made on the ‘unforced variations’ thread.“(C)limatologists don’t look beyond the troposphere and take into account the energy inputs from space weather as being a significant driver of climate change” because such cosmic energy inputs aren’t significant drivers of climate. See Section 6.2 or the rather busy Fig 13 in Lacis et al (2013). Note that to cosmic element is the smallest of the non-solar energy sources. I don’t know what proportion of that insignificant part would be changed by a reduction of the Earth’s magnetic field, but I’m not holding my breath.
As for suggesting to me that there has been a ‘hiatus’ in global temperature for the last 15 years, I have to ask which globe is it you are talking about? Not planet Earth!
Earth’s average temperature has been flat for perhaps 7 years. Prior to that, the rate of rise was accelerating, which sort of makes a nonsense of any foolish argument to the contrary. I link to a graphic here (usually 2 clicks to ‘download your attachment’) which illustrates the point rather well. If the slope of the temperature rise is increasing (plotted in the red trace), that would be an aceleration.
Of course, the surface temperatures may have been flat since 2007 or so but the oceans who always grab the lion’s share of the warming, they continues to warm at an increased pace. So the warming has not stopped. It is rather ‘otherwise engaged’.

re: 81 Rodgers and my post 61. You say you tried to replicate my statistical analysis and did not get the same answer. What do you actually do? Without further information, I can only assume that you made mistakes. Maybe you can send me the analysis.

I can send you mine. I did an OLS Granger, with differences of logs, using monthly sea ice extent in the arctic and antarctic, with month dummies with 24 monthly lags. I got big negative effects with the antarctic as DV over about lags 4-12, but no effects with arctic as DV.

My post 61, if anywhere near correct, would explain much of what puzzles climate science about what is happening at the poles.

re: 81 and 61, continued. MA Rodgers – A further point is that there are two months of missing data in the ice extent data series. These have to be estimated for the Granger to work properly. I did that by averaging the data points for the same month in the prior and succeeding years.

t marvell @83/84.
Our understanding improves with leaps and boutds. So your “strong statistical link” was obtained from a Granger causality test, the test which Granger himself cautioned that “Unfortunately, many users concentrated on this forecasting implication rather than on the original definition” and that “any applied researcher with two or more time series could apply it … Of course, many ridiculous papers appeared.”
I should stress that even now I am still far from clear on what it is you have adopted for your input functions. So you will forgive me if I fail to begin scrabbling round trying to recreate a Granger test on something to do with Arctic & Antarctic SIE. Indeed, it would be sensible if you pause awhile and then explain what it is you have done with the data, the results of that manipulation and what you think are the implications of those results. Perhaps we can then determine if it is worthy of discussion or if it is “ridiculous.” You do not need to “send” anything to anybody. Rather explain the details in plain English here on this thread. And trust me – if you cannot explain your work to others, it is very very likely you do not understand it yourself.
I would however say that I remain bemused by all this. If there were a causal one-way link from Arctic SIE to Antarctic SIE of great significance as you suggest, it should be child’s play to demonstrate it without recourse to Granger.

MARodger @82 Thank you for taking the time to respond, and with links that I will add to the learning curve… The A. A. LACIS ET AL. paper eloquently illustrates the sensitivity of the anthropogenic quotient in climate change.

Are you seriously asking us to believe that anthropogenic forcing is 114 W/m2?

Thanks Gavin, but it looks to me like PabloNHp is asking about the global anthropogenic forcing, which I took from AR4. And he’s got me: The IPCC estimates the sum of positive and negative global RF averages 1.6 W/m2, so I was off by two decimal places. It’s a good thing I don’t claim to be a climate expert myself 8^}!

So, the geothermal heat flux under the Thwaites glacier is really around a tenth of the global anthropogenic radiative forcing. However, inline to Victor’s suggestion that undersea geothermal heat flux might be comparable to anthropogenic forcing globally, Prof. Steig supported the point I wanted to make:

[Response: I am 99.995% confident this isn’t important. That UTIG study is greatly misinterpreted — there is not evidence of an important *change* in the amount of volcanic activity; that paper only shows that the sub-ice heating is large. The bottom of the ice sheet cares about this because it is an important local source of heat. The ocean does not care about this — we’re talking the difference between W/m^2 from the sun, vs. milliwatts from heat from the ocean bedrock.—eric]

Thwaites is thinning. Bedrock elastic rebound is immediate, plastic is delayed. But i wonder now about heat conduction in stressed vs. unstressed bedrock. And the heat generated as rock deforms as stress is relieved. Probably small compared to basal melt from ocean heat flux, but …

The Holland(2014) paper does not use melt from AIS at all, and reproduces observation. Would it be possible to include this easily in the MIT GCM they used for the Southern Ocean ? They do include the seasonal freshwater flux from sea ice, ten times larger, so this would seem “easy” … i wonder if they did so and observed no difference, but i suppose they would have mentioned. So this seems to say that the MIT GCM is superior to EC-Earth used in Bintanja for Southern Ocean, not too surprising since it is probably several years more advanced.

melting (conversion of solid into liquid) or sublimation (conversion of solid into vapor). Both transformations require energy. It takes 8.5 times as much energy to convert a kilogram of ice into water vapor by sublimation as it does to convert the same kilogram into liquid water by melting.

Re: posts 85 & 86, about the possibility that there is a link between Arctic and Antarctic sea ice extent through the THC (post 61), which would explain why Arctic ice extent has declined more than expected and why Antarctic ice extent is growing.

The timing is tight. My post 61 implies that the deep THC in the Atlantic moves at least 20cm/sec, at the upper limit of estimates. It could be that the THC is speeding up, bring more cold water in.

The volume of water in the THC is probably enough. The volume of water flow is about that of all rivers on earth. The THC seems to have large effects generally. The SST’s in the Northern and Southern hemispheres affect each other greatly (in the positive direction), with lags of around a year. The THC is probably the best explanation for that, and that would take a huge volume.

About the Granger test – the quote in #86 is not applicable. I’m not using the test to forecast. The Granger test tests priority in timing, and it does not imply a direct mechanism. There could also be spurious correlation, both north and south ice caused by some third factor (that operates on Southern ice without delay). The test is highly suggestive, but not proof. An important issue is whether the climate models predict such a connection between North and South ice.

Rodgers says “If there were a causal one-way link from Arctic SIE to Antarctic SIE of great significance as you suggest, it should be child’s play to demonstrate it without recourse to Granger.” How? The implication is that if there is another way to demonstrate a link, it would also be useful in refuting it.

About the specifics of the analysis. Again, I use monthly data for the Northern and Southern ice extent (since 1978). I log and difference the variables. The Granger involves two regressions, with the North the DV in one, and the South the DV in the other. On the right side of both equations are lags of both North and South ice changes. The coefficients on the IV lags are use to test “causal direction.” The regressions include monthly dummies to control for seasons. I originally used lags of 24 months, but I now find, using the BIC for the lagged IVs, that 17 lags is best. Changes in the North ice “affects” (that is proceeds) South ice changes by about 4 to 12 mo. South ice does not “affect” North ice.

A further, important point is that the North and South ice extents are cointegrated (I ran the cointegration tests with monthly anomalies and with annual data.) That is probably the strongest statistical test of a causal relationship between two time series. It does not indicate which variable causes which, or the timing of the causal effect. The relationship is negative, based on the Granger test results and on highly significant negative correlations between the two variables. Simple correlations are meaningful in this case because the variables are cointegrated.

t marvell @94.
We’re not getting very far here.
The description you give of the two time series you analyse using Granger remains deficient. But let us cut to the chase. You tell us:-

“Rodgers says “If there were a causal one-way link from Arctic SIE to Antarctic SIE of great significance as you suggest, it should be child’s play to demonstrate it without recourse to Granger.” How? The implication is that if there is another way to demonstrate a link, it would also be useful in refuting it.”

I’m with Rodgers on this one, whoever Rodgers is. To “demonstrate” this alleged relationship will not require the same rigour required when ‘establishing’ such a relationship. You tell us that waggles in monthly Arctic SIE result in waggles monthly Antarctic SIE over following months. So plot those waggles in Arctic & Antarctic SIE suitably lagged and adjusted to show visually this “highly significant negative correlations between the two variables.” Simples.
And I suppose if such a “demonstration” were not possible, then yes, implicitly it would rather suggest there is a problem with your analysis.

re post 85: I don’t know of any way to graph these relationships. Cointegration means a general movement of two variables in the same (or opposite) direction, such that a linear combination does not change greatly.

Plotting a causal spread of some 8 monthly changes is likewise difficult.

A lot of times visual representations are not feasible. Certainly you would never ask for a visual representation of a climate science computer model.

One can get a general idea of what cointegrated variables look like in graphs of Arctic and Antarctic sea ice trends. See climate4you.com Sea Ice page, graph “Sea ice extension in a longer time perspective” The Arctic and Antarctic plots generally move in opposite directions. But such a visual representation is slight evidence of cointegration.

By the way, CO2 and global temperature are cointegrated. There is no stronger evidence of a connection between the two.

An interesting point is that Northern (64-90N) and Southern (64-90S) temperatures move in the same direction – that is, warming – the opposite from the sea ice relationship. I suspect that the reason is that warming is on the side opposite to where the THC hits Antarctica and to where sea ice is increasing the most.